During the coming year we hope to characterize D-cell function in man. After one year of effort, we have yet to develop a practical radioimmunoassay for somatostatin in unextracted human plasma, as we had done previously in dogs. We have defined certain of the technical obstacles to such an assay and it appears that rapid degradation of endogenous somatostatin, coupled with proteolytic damage to the somatostatin tracer, constitute the main obstacles. We plan to test the efficacy of four extraction or isolation technics by which to circumvent the problems of whole plasma assay. These include gel filtration, acetone extraction, immunoaffinity chromatography and ion exchange chromatography. The best recoveries have thus far been observed with immunoaffinity chromatography methods. Our efforts now are designed to make such technics practical for large volume assay work required for physiologic and pathophysiologic studies in man. If and when this is accomplished, we plan to study the somatostatin response to meals and to other maneuvers in normal subjects and in obese subjects as well as in the various forms of diabetes, in gastrointestinal disorders and pituitary disease. Our interest in this problem is prompted by the possibility that somastatin, as the regulator of nutrient movement of the gut lumen to the internal environment, may be important in a broad spectrum of human disorders. In collaboration with Drs. Raskin and Pietri a clinical study of the efficacy of metabolic near-normalization of Type I diabetics upon muscle capillary basement membrane thickness, renal function, motor nerve conduction velocity, HDL-2 and LDL levels, and retinal fluorescin angiography will continue into its second year.